Denser Media means velocity of wave considered is less then the velocity in other medium (rareer medium)

For  sound

   v =sqr root(B/d)   [where B is Bulk Modulas and d is density]

formula tells that V_sound in air is less(many times) than in water hence it(air) is denser wrt water

and

 for light

 we know it is V _water V_air /  

that is ,speed is less in water and hence it is a denser media wrt air

hoorey !! we have done it

kuch samajh mai aaya ?